Magnetic material



Oct. 29, 1963 P. G. FRISCHMANN ETAL I 3, 5

' MAGNETIC MATERIAL Filed 00';- 5, 1960 F .2. lg

In ventor's: Peter- G:7=r-/'schmahn, (JO/777.44. W /)1 Th e/r Attorney- United States Patent 3,108,912 MAGNETIC MATERIAL Peter G. Frischrnann, Phoenix, Aria, and John L. Walter, Scotia, N.Y., assignors to General Electric Company, a corporation of New York Filed Oct. 5, 1960, Ser. No. 60,720 4 Claims. (Cl. 148-3155) This invention relates to bodies of magnetic alloys for use in induction apparatus and more particularly to high purity silicon iron alloys having unique magnetic properties and to a process for producing these bodies.

In the construction of the many types of induction apparatus, magnetic materials having diverse and often special magnetic properties are required. The applications in which any given magnetic material may be used depend upon such properties as the coercive force, permeability and residual induction. Heretoi'ore, the construction and operation of certain types of communications equipment, for example, have required the use of special alloys or specially constructed bodies to achieve essential magnetic properties. Specifically, for such uses as filter coils in radio and television circuits and as loading coils for long distance telephone transmission lines, the permeability should be substantially constant and the eddy current losses low, particularly at low field strengths, to obtain true reproduction of sound. Early attempts to attain constant permeability involved the use of concentrated air gaps in the core, but these attempts were generally discontinued due to the efiects of flux leakage upon the surrounding circuitry. Although the permeability of ferromagnetic materials is inherently not constant, fair success in obtaining constant permeability was achieved by using compressed iron powder. The iron powder particles were used both insulated and uninsulated, the former giving somewhat lower values of permeability than the latter and also having much lower eddy current losses. The permeabilities of these materials ranged from about 25 to 75 at inductions (B) of up to 100 gausses.

Higher values of constant permeability of up to 2,000 at inductions of up to 1,000 gausses have been achieved in special types of relatively expensive high alloy metals. For example, the Perminvars, which are alloys usually containing from about to 55 weight percent nickel, to 60 weight percent cobalt, remainder substantially all iron, have substantially constant permeability but the particular metals used render them comparatively expensive. The Perminvar composition ranges listed are not intended as limiting since other proportions of the constituent metals may deliver suitable properties for some uses. Further information regarding Perminvars and related alloys can be obtained from publications such as Ferromagnetism, by Richard M. Bozorth, published in 1956 by D. Van Nostrand Company, Inc.

A principal object of this invention is to provide bodies of silicon-iron alloys having substantially constant magnetic permeability.

Another object of this invention is to provide ironbase bodies containing from 4 to 6 weight percent silicon which have substantially constant permeabilities in low magnetic fields.

A further object of this invention is to provide siliconiron alloy bodies oriented in the (110) [001] crystalline orientation, which bodies have substantially constant magnetic permeability.

An additional object of this invention is to provide a process for producing silicon-iron alloy bodies having substantially constant magnetic permeabilities.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification and drawings.

3,108,912 Patented Oct. 29, 1963 ice In the drawings:

FIG. 1 shows hysteresis curves for oriented siliconiron alloy bodies used to produce bodics'according to the present invention;

FIG. 2 shows hysteresis curves of the unique bodies of this invention; and

FIG. 3 shows the hysteresis curves of the bodies of FIG. 2 following additional treatment.

Generally, the bodies of the present invention are made of high-purity iron-base alloys containing from 4 to 6 weight percent silicon and not more than about 0.01 Weight percent incidental impurities. These bodies, when processed according to the method of the invention, have substantially constant magnetic permeabilities. The novel process of this invention comprises preparing a highpurity alloy of the composition previously mentioned and processing it through a plurality of hot and cold rolling stages with intermediate anneals to develop a strong (110) [001] crystalline orientation. The oriented bodies are then given a final anneal in selected atmospheres to produce the constant permeability.

Considering the processing in more detail, cast ingots are prepared by vacuum melting high-purity iron and silicon together in proportions such that the silicon content of the final alloy falls between 4 to 6 percent. The impurity content of the cast alloy should not exceed 0.010 weight percent as a maximum and should preferably not exceed more than about 0.006 weight percent. The normal content for some of the more usual impurities is carbon, 0.001; sulfur, 0.001; oxygen, 0.001; and nitrogen, 0.0005; the remainder being minor metallic impurities which are normally present.

Once a cast ingot is obtained, it is hot rolled to 0.25 inch. At this point, the material is annealed at 700 C. to 1200 C. for-from about 0.1 to 1.0 hour in dry hydrogen, that is, hydrogen which is substantially nonoxidizing to silicon, viz., dew point no higher than 40 F. The slabs are then rolled at from 700 to 1000 C. to about 0.100 inch thickness. The material at this stage is subjected to an annealing at temperatures ranging from about 700 C. to 1200" C. for a time sufficient to recrystallize the hot-worked texture, e.g., about 0.1 to 10 hours in a substantially nonoxidizing atmosphere such as dry hydrogen. It is to be understood that all reference to dry hydrogen means hydrogen having a dew point no higher than 40 F., unless specified to the contrary.

The annealed product is then cold worked at least 25 percent in substantially the same direction (e.g., over the range of 40 percent to 99.5 percent) using intermediate anneals where required when more than one reduction stage is used to arrive at thicknesses ranging up to about 0.015 inch. The intermediate anneal which is also carried out under substantially nonoxidizing conditions may range in temperature from about 700 C. to 1200 C. for a time sufficient to effect recrystallization, such as 0.1 hour to 10 hours.

After the final thickness has been reached, the coldworked material is then subjected to an anneal at an elevated temperature in a selected environment for a suificient time to effect secondary recrystallization. Temperatures for the final anneal may range from about 1000 C. to 1350 C. for times ranging up to about 16 hours for thicknesses ranging up to about 0.015 inch, the annealing time increasing with increasing thickness and decreasing with increasing temperature. Generally, times as low as 1 hour are adequate at the high temperatures. Suitable environments for use during the final anneal include hydrogen having a dew point no higher than about F. and vacuum, pressures no higher than 1 10 mm. of mercury being suitable. Lower pressures are especially advantageous, for example, pressures on the order of 6x10 Further information regarding suitable methods for producing high-purity cube-on-edge grain oriented silicon-iron bodies can be obtained from the pending application of John L. Walter, Serial No. 59, filed January 4, 1960, and assigned to the same assignee The development of the sheared loop or constant permeability which is so unique to this alloy is believed caused by the diffusion of minor amounts of oxygen into the alloy body during the final anneal. In the example as the present application. 5 just given, it is believed that there is a reaction between To produce bodies of silicon-iron having constant perthe hydrogen of the annealing atmosphere and the mea bility, the cube-on-edge or (110) [001] grain Ori nt d alumina plates which either produces a small amount of material is subjected to another anneal at temperatures oxygen or a small amount of water vapor which, when ranging from about 1000 to -l 350 C. (for times of not contacting the surface of the silicon-iron, decomposes into less than about one-quarter hour. This anneal is caroxygen and hydrogen. The oxygen then diffuses into the ried out in such a Way that the bodies are subjected to body of the material, causing the change in magnetic the presence of a minor amount of oxygen, th oxygen proper-ties. It is believed that the oxygen can be supplied being 'felt responsible for the achievement of the unique by means other than alumina plate as, for example, by magnetic properties. A dry hydrogen atmosphere can be providing a small amount of free oxygen in the hydrogen used for this a al a xygen introduced aCC P atmosphere during annealing. Test results indicate that the desired properties. An alumina supporting plate has it the material is annealed in dry hydrogen alone, no been found efiective in supplying the required oxygen, as change in the magnetic properties is obtained. Similarly, later shown. At the termination of this anneal, the the properties remain unchanged if the material is placed samples are cooled at the rate ranging from about 50 to on plates of alumina and annealed in an argon atmos- 200 C. per hour. phere at the same temperature.

As an example of bodies produced according to the In an effort to determine the means by which the conpresent invention, an initial body of 0.012 inch thickness stant permeability is obtained and specifically to deter- Was produced according to the procedure outlined earlier, mine whether the effect was caused by an oxide layer at and after the final reduction to 0.012 inch, was annealed the surface of the alloy specimen which exerted compresat 1200 C. in a vacuum at a pressure of about 6 X10- sive or tensile stresses on the material, the samples were mm. of mercury for 6 hours. This heat treatment caused electropolished to remove about 1 mil from the over-all the samples to orient in the (110) [001] crystalline thickness of the specimens. FIG. 3 of the drawings orientation as evidenced by the hysteresis loops 10 and 11 shows D.-C. hysteresis loops obtained from the same shown in FIG. 1 of the drawings. The D.-C. properties specimens used to produce the figures of 1 and 2 and it of the samples corresponding to curves 10 and 11 are is readily apparent that the sheared loop or constant perlisted in Table I below: meability properties are still present. In fact, While the Table I properties of the sample indicated by curve 14 are very similar to the properties indicated by curves 12 and 13, I d a at there seems to have been some improvement in the con- Coercive Force Ind 11 (g Max stancy of the permeability of the sample Whose properties in oer. Br 1 IH) are indicated by curve :15. The coercive force and other (Gausses) 5 f Perm magnetic properties of the samples following electropolishing are contained in Table III.

9 3:8ia:::::::::::::::::: it??? iii 133 iiiti 11323 iiiggg 4.0 Table 111 It should be noted that the coercive force of the ma- Induction (gausses) at terial at this stage is quite low, while the residual inducgg g gg g E tion and the induction in fields of /2, 1 and 2 oersteds (Gausses) H=% H=l H=2 Perm. are comparatively high.

Following the production of the grain oriented bodies, the samples were thenplaced on a h -P alumina 31335::331223131333: ""3 iiid 3:528 13318 $33 supporting plate and given an additional anneal 111 day hydrogen (dew point 60 F.) at 1200 C. for one hour and then cooled at the rate of 100 C. per hour to about It is thus pp that the pr nt invention provides 200 C. These samples are the same ones which were a I10Ve1 Process and magnetic body having Pwperties used to obtain the hysteresis loops showninFIG. 1. The wh have not Previously been Obtained in -base specimens, upon once again being subjected to applied sihcon alloys. The constant permeability obtained in this magnetic fields, had magnetic properties indicated by comparatively common and relatively cheap ma'ifiriall Will curves 12 d 13 i FIG, 2 d li ted i T bl II 5 have many uses in those applications where heretofore following; only expensive specialty alloys have been found adapt- Table 11 able- What we claim as newand desire to secure as Letters induction (misses) Patent of the United States is:

Coercive Force Res. Ind. Max. 1. An article of manufacture comprising, a high-purity o ((353895) H=% 13:1 11:2 34 3 alloy body having a majority of its constituent grains oer. oer. oer. oriented in the (.110)[001] crystalline orientation and consisting of from about 4 to 6 weight percent silicon,

0.025 1,500 6,600 8,550' 14,250 4,700 remainder substantially all iron, and containing not m M25 L000 @000 {NW 6500 than about 0.010 weight percent incidental impurities,

said body having substantially constant magnetic permea ability when subjected to applied magnetic fields of from about 0.1 oersted to fields wherein induction approaches saturation.

2. An article of manufacture comprising, a high-purity alloy body of up to 15 mils thickness having a majority of its constituent grains oriented in the [001] crystalline orientation and consisting of from about 4 to 6 weight percent silicon, remainder substantially all iron, and containing not more than about 0.010 weight percent incidental impurities, said body having substantially constant magnetic permeability.

3. An article of manufacture comprising, a high-purity alloy body of up to 15 mils thickness having a majority of its constituent grains oriented in the (110) [001] crystalline orientation and consisting of from about 4 to 6 weight percent silicon, remainder substantially all iron, and containing not more than about 0.010 weight percent incidental impurities, said body having substantially constant magnetic permeability when subjected to applied fields of up to about 2 oersteds.

4. An article as defined in claim 1 wherein said impurity content does not exceed 0.006 Weight percent.

References tilted in the file of this patent UNITED STATES PATENTS 1,569,355 Cole Jan. 12, 1926 1,932,308 Freeland Oct. 24, 1933 2,242,234 Carpenter May 20, 1941 2,535,420 Jackson Dec. 26, 1950 2,875,113 Fitz Feb. 24, 1959 2,939,810 Fiedler et a1 June 7, 1960 OTHER REFERENCES Ferromagnetism: Bozorth, 1951, D. Van Nostrand Co., Inc, pp. 35, 36, 6063 and 83-86 relied upon. 

1. AN ARTICLE OF MANUFACTURE COMPRISING, A HIGH-PURITY ALLOY BODY HAVING A MAJORITY OF ITS CONSTITUENT GRAINS ORIENTED IN THE (100)(001) CRYSTALLINE ORIENTATION AND CONSISTING OF FROM ABOUT 4 TO 6 WEIGHT PERCENT SILICON, REMAINDER SUBSTANTIALLY ALL IRON, AND CONTAINING NOT MORE THAN ABOUT 0.010 WEIGHT PERCENT INCIDENTAL IMPURITIES, SAID BODY HAVING SUBSTANTIALLY CONSTANT MAGNETIC PERMEABILITY WHEN SUBJECTED TO APPLIED MAGNETIC FIELDS OF FROM ABOUT 0.1 OERSTED TO FIELDS WHEREIN INDUCTION APPROACHES SATURATION. 